DIPLOMATS from six world powers offered Iran new proposals today to ease international concerns about its nuclear programme, but appeared to reject Tehran's appeals to ease economic sanctions.

The proposal by the US and its negotiation partners - the UK, China, Russia, France and Germany - focused on Iran's highest-level uranium enrichment.

Many world leaders fear the 20% enrichment could be quickly turned into warhead-grade material.

The proposal could meet a swift refusal from Iran. Its envoys want agreements to lessen, or at least delay, sanctions that have targeted critical oil exports and cut off the country from lucrative European markets.

Mike Mann, spokesman for the head of the European Union delegation that is leading the talks in Baghdad, told reporters: "We hope the package that we put on the table is attractive to them so they will react positively. It's up to them to react."

Mr Mann would not discuss whether the 20% enrichment represented a red line that could again scuttle the negotiations, which only restarted last month after collapsing early last year.

The high-enriched uranium is far above the level needed for energy-producing reactors, but is used in medical research. Iran claims its nuclear programme is only for electricity and medical applications.

Tehran has tentatively agreed to allow UN inspectors to restart investigations into a military base with suspected links to nuclear arms-related tests. Mr Mann expressed cautious optimism about the still-unsigned deal with the International Atomic Energy Agency, but said it would have little bearing on today's talks.

Despite the new proposals, no breakthrough accords are expected in the talks in Iraq's capital, suggesting that all sides are still shaping their strategies and the negotiation process is likely to be long.

That could allow US and European allies to significantly tone down threats of military action, but it would be likely to bring objections from Israel, which claims Iran is trying to buy time to keep its nuclear fuel labs in full operation.

Mr Mann suggested that any rollback in sanctions was unlikely in the Baghdad talks. He said some of the most painful sanctions - including a European Union ban on Iranian oil imports beginning on July 1 - are a "matter of the law and they will come into force when they come into force".

The Obama administration has been vague about its immediate goals, with officials saying the talks will gauge Iran's seriousness and explore elements of a possible agreement. A Western diplomat in Baghdad said the talks will focus on "confidence-building measures" that Iran's nuclear programme is only being used for peaceful purposes.

Washington has shown little willingness to bargain, despite the tentative IAEA agreement to inspect the Parchin military complex south east of Tehran. That is where the UN believes Iran ran explosive tests in 2003 needed to set off a nuclear charge. Tehran says Parchin is not a nuclear site.